1. Field of the Invention
The present invention relates to a reflective electrode and a compound semiconductor light emitting device, and more particularly, to a reflective electrode with low contact resistance, high reflectance, and improved electrical conductivity, and a compound semiconductor light emitting device including the same.
2. Description of the Related Art
Compound semiconductor light emitting devices, for example, semiconductor laser diodes such as light emitting diodes (LEDs) and laser diodes (LDs), convert electric signals into optical signals using the characteristics of compound semiconductors. Laser beams of the compound semiconductor light emitting devices have practically been applied in the fields of optical communications, multiple communications, and space communications. Semiconductor lasers are widely used as light sources for data transmission or data recording and reading in the field of optical communications and such apparatuses as compact disk players (CDPs) or digital versatile disk players (DVDPs).
A compound semiconductor light emitting device can be categorized into a top-emitting light emitting diode (TLED) and a flip-chip light emitting diode (FCLED) according to the emission direction of light.
The TLED emits light through a p-type electrode, which forms an ohmic contact with a p-type compound semiconductor layer. The p-type electrode includes a Ni layer and an Au layer, which are sequentially stacked on a p-type compound semiconductor layer. However, since the p-type electrode formed of the Ni layer and the Au layer is translucent, the TLED including the p-type electrode has low optical efficiency and low brightness.
In the case of the FCLED, light emitted from an active layer is reflected by a reflective electrode formed on a p-type compound semiconductor layer, and the reflected light is emitted through a substrate. The reflective electrode is formed of a material having good optical reflectance, such as Ag, Al, and Rh. The FCLED including this reflective electrode can have high optical efficiency and high brightness. However, owing to a relatively high contact resistance between the reflective electrode and the p-type compound semiconductor layer, a light emitting device including the reflective electrode has a shortened life span and unreliable characteristics.
To solve these problems, research on materials and structures for an electrode having low contact resistance and high reflectance has progressed.
International Patent Publication No. WO 01/47038 A1 discloses a semiconductor light emitting device including a reflective electrode, which is provided with an ohmic contact layer disposed between the reflective electrode and a p-type compound semiconductor layer. However, the ohmic contact layer is formed of a material having low optical transmissivity, such as Ti or Ni/Au, thus degrading optical efficiency and brightness.